Current experimental techniques have allowed the manipulation of atomic systems to previously unthinkable degrees, paving the way to the development of new technologies and the observation of very small quantum effects. One such technologies is the quantum computer; trapped ions systems have been implemented successfully to perform logical operation [1]}, [2]}, [3]} making atomic systems a strong candidate for scalable quantum bits. Furthermore, the implementation of highly excited states (Rydberg atoms) has been proposed for quantum computing because of the length of their interaction and their long coherence times [3]}, [5]}, [6]}, [7]}. In order for atoms be suitable for quantum technologies it is necessary for them to have long coherence times, which is ultimately limited by their interaction with environmental particles [8]}. In this paper we propose a new decoherence mechanism of excited atomic systems induced by particles through short-distance interactions. This would not only presents a fundamental limit to the stability of atomic systems, but also can be applied to the detection of weakly-interacting particles by means of analyzing the evolution of the atomic state. A search for exotic interactions using the decoherence of a Ramsey interferometer has been suggested previously [9]}, [10]}, however the mechanism for linking the decoherence of internal degrees of freedom of the atom (energy levels) with momentum transfer was left open.
In our work, we propose that when a particle is scattered by the atomic nucleus it will produce an almost instant change in the position of the nucleus which will be perceived by the electron in the atom as a sudden change in the electrostatic potential, projecting the wave function of the atom into the eigenstates of the new potential.
First we calculate the change in the state of the atom as a result of the nuclear displacement, obtaining a projection over lower energy levels only. We then express the order of the displacement in terms of the properties of the nucleus and the scattered particle, observing that the effect is more prominent for Rydberg atoms. Finally, we extend the analysis to multiple scattering events and analyze the evolution of the state of an atom scattering photons and massive particles.
